imalion – creation and low energy transportation...
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IMALION - CREATION AND LOW ENERGY TRANSPORTATION OF A
MILLIAMPERE METAL ION BEAM∗
T. Weichsel† , U. Hartung, T. Kopte, Fraunhofer FEP, Dresden, Germany
G. Zschornack, Dresden University of Technology and
Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden, Germany
M. Kreller, A. Silze, DREEBIT GmbH, Grossroehrsdorf, Germany
Abstract
IMALION - which stands for IMplantation of ALu-
minum IONs - is a facility designed for high-current metal
ion beam implantation and surface modification such as in
semiconductor, medical or optical industry. IMALION is a
newly developed 30 kV metal ion wide area implantation
platform, which is suitable for the irradiation of a target
width of 200 mm to produce homogeneous implantation
profiles over the entire surface. Electrostatic and magnetic
beamline elements such as a deflector as well as analyz-
ing and parallelization magnets were designed for precision
guiding of a milliampere metal ion beam. The implanter is
fed by a novel ECR metal ion source, which is equipped
with an integrated cylindrical sputter magnetron as metal
vapor supply. Stable operation of the sputter magnetron un-
der ECR magnetic mirror conditions was proven by optical
emission spectroscopy and Langmuir probe measurements.
INTRODUCTION
The aim of the IMALION project is to develop a new high
current metal ion source together with a wide area metal
ion implantation platform suitable for substrate widths of
200 mm and scalable to 2 m for large surface applications
in semiconductor, optical and medical industry. Proof of
principle experiments are conducted with Aluminum ions
as they can show the significant advantage of the system
in the field of photovoltaics. The new solar cell generation
based on n-type silicon wafers utilizes p-type emitter lay-
ers usually generated by thermal diffusion of Boron from
gaseous compounds. As an alternative, Al ion implantation
out-performs the diffusion procedure as one can achieve a
well defined doping level and profile together with better ho-
mogeneity and reproducibility as well as higher purity. Fur-
thermore, the number of process steps is reduced because
there is no need for edge isolation and parasitic glass layer
removal [1–3]. As Boron is replaced by Aluminum the use
of toxic B-containing starting materials can be avoided.
MAGNETRON ECR ION SOURCE
A new high-currentmetal ion source prototype was devel-
oped. It combines magnetron sputter technology with elec-
tron cyclotron resonance (ECR) ion source technology — a
so-called Magnetron ECR Ion Source named “MECRIS”
∗ Work supported by the European Fund for Regional Development of the
European Union and the Freistaat Sachsen under Grant Nos. 100106678
and 100096350† [email protected]
(Fig. 1). An integrated inverted cylindrical sputter mag-
netron is acting as a metal atom source with a ring shaped
Al cathode with an inner diameter of 200 mm, a width of
50 mm, and a thickness of 10 mm. The cathode is part of the
chamber wall of the cylindrical ion source volume with a ra-
dius of 100 mm and a length of 200 mm. The ECR plasma
is sustained by injection of microwaves with a frequency of
2.45 GHz in TE10 mode through a rectangular waveguide
and it is used to ionize the metal atoms by electron impact.
In order to protect the quartz glass microwave transmitting
window from Al vapor deposition it had to be placed be-
hind a 90° elbow element of the waveguide. Mostly singly
charged Al+ metal ions and ions of the process gas (Ar+,
Kr+ or Ne+) are extracted through a one hole aperture with
a variable diameter of 4 mm to 10 mm by a 3 electrode sys-
tem of the accel-decel-type. The MECRIS is operated on
a 30 kV platform so that Al+ ions with a maximum kinetic
energy of 30 keV can be implanted into the grounded target.
solenoid coils
extraction
system
microwave window
and waveguide
double
Langmuir probe
sputter magnetron
200 mm
Figure 1: Sectional view of the ECR ion source with inte-
grated cylindrical sputter magnetron.
The magnetic field used to confine the plasma inside the
ion source is produced by a pair of solenoid coils and by the
permanent magnets of the sputter magnetron. Depending
on the coil current (max. 200 A each) an off-axis minimum-
B-field-structure is obtained, which contains a closed mag-
netic flux density surface at 87.5 mT satisfying the ECR con-
dition (Fig. 2). Spatially resolved double Langmuir probe
and optical emission spectroscopy measurements show an
increase in electron density by one order of magnitude from
1 × 1010 cm−3 to 1 × 1011 cm−3 when the magnetron
Proceedings of IPAC2014, Dresden, Germany MOPRI085
04 Hadron Accelerators
T01 Proton and Ion Sources
ISBN 978-3-95450-132-8
809 Cop
yrig
ht©
2014
CC
-BY-
3.0
and
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-80
-40
0
40
80
0
40
80
120
160
200
010
20
30
40
50
60
70
8090100
110
120
minimum B
electronconfinement
length [mm]
B [
mT
]
radius [mm]
01224364860728496108120
axis ofrotation
Figure 2: COMSOL - FEM - simulation of magnetic flux
density of z - r cut plane of the MECRIS. Coil current com-
bination 150 A / 135 A.
plasma is exposed to the minimum-B-field of the ECR ion
source. A detailed study of electron temperature and den-
sity of the magnetron plasma as well as the magnetic field
design of the MECRIS was published elsewhere [4]. Ex-
perimental investigation of the plasma parameters of the
MECRIS plasma will be published separately.
IMALION IMPLANTER
The IMALION implantation platform is fed with an Al+
ion beam from the MECRIS and uses a magnetic steerer to
guide the beam into a double-focus analyzing dipole mag-
net, which separates the process gas ions from the Al+ ions.
After this, an electrostatic deflector is used to scan the Al+
ion beam into a parallelization dipole magnet, which pro-
duces parallel Al+ ion beams impacting on the substrate
surface. In this way, the entire surface of a substrate with
a width of 200 mm is implanted by scanning the beam in
horizontal direction and by upward or downward movement
of the substrate (Fig. 3). All beamline elements of the
IMALION implanter were designed for precision guiding
of a 30 mA Al+ ion beam using the FEM simulation soft-
ware Field Precision [5]. Because of the wide ion beam
cross section the effect of coulomb repulsion of the Al+ ions
was neglected.
Analyzing Magnet
Filtering of the Al+ ions from the process gas ions Ar+,
Kr+ or Ne+ and ions of the background gas is achieved by
a 90° q/A analyzing dipole magnet with q being the charge
state and A the atomic mass. For the simulation of the mag-
netic field and the ion trajectories a pole gap of 80 mm, a
bending radius of 250 mm as well as a beam diameter of
15 mm was used. The magnet pole shoes were designed to
approximate a Rogowski profile with two level stages at dif-
ferent angles [6]. Two dimensional focusing is achieved by
tilting the front and rear faces of the pole shoes in relation
magnetron
ECR ion
source
steerer
90° analyzing
magnet
electrostatic
deflector
magnetic beam
parallelization
target
ca. 3m
ca. 4m
Figure 3: Design of the IMALION facility for Al+ ion im-
plantation into large area substrates via ion beam scan op-
tics.
to the beam line axis by 33°. The analyzing magnet was
optimized for a 30 mA and 30 keV Al+ ion beam. It is able
to resolve 27Al+ from 28N+2 , which was the most critical
precondition in terms of q/A resolution.
Ion Beam Scan Optics
After the analyzing magnet the beam passes an electro-
static deflector. It consists of two electrodes with the shape
of a half cylinder cut diagonally in relation to the beam di-
rection. In this way, a compact system was designed that
is able to deflect the beam by ± 10° using electrode poten-
tials with a difference of maximum 8 kV. Additionally, the
deflector works as an electrostatic lens when it is operated
with a potential offset of a few kV above ground potential.
Then the deflector focuses the scanned beam into the paral-
lelization magnet (Fig. 4).
-250 2
50
-1000 1000y [mm]
x [
mm
]-2
50 250
x [
mm
]
-2.85E+04
2E+03
-1.33E+04 [V]
(a)
(b)
Figure 4: FEM simulation of electric potential as well as
Al+ ion beam displacement by the electrostatic deflector.
(a) - lens potential 0 V, deflection potentials ± 2 kV. (b) -
lens potential -25 kV, deflection potentials ± 3.5 kV.
MOPRI085 Proceedings of IPAC2014, Dresden, Germany
ISBN 978-3-95450-132-8
810Cop
yrig
ht©
2014
CC
-BY-
3.0
and
byth
ere
spec
tive
auth
ors
04 Hadron Accelerators
T01 Proton and Ion Sources
-11
00
1
00
-100 1100y [mm]
x [
mm
]
0
1.1E-01 [T]
2.6E-01
Figure 5: FEM simulation of magnetic flux density as well
as Al+ ion beam parallelization with the dipole magnet.
The parallelization magnet produces parallel Al+ ion
beams in horizontal direction over a width of 200 mm to
irradiate a substrate perpendicular to its surface (Fig. 5).
The magnet uses a beam bending angle of 45°. The beam
meets the front face of the magnet perpendicularly under
each deflection angle. At the exit, the pole shoe face is tilted
in relation to the beam axis by an angle, which is equal to
the respective deflection angle. Furthermore, a pole gap of
80 mm and a deflection radius of 500 mm were used for the
simulations.
The combination of deflector and parallelization magnet
as an ion beam scanning unit is suitable to provide a ho-
mogeneous Al+ ion dose of 2.25×1016 cm−2 ± 0.1% at
an Al+ ion current of I = 30 mA with an average beam
spot size of 41.0 mm ± 0.8 mm in vertical direction and
23 mm ± 4 mm in horizontal direction (Fig. 6). For a ho-
mogeneous dose over the entire substrate surface, it is im-
portant that the beam spot hight varies as little as possible in
the direction of the substrate movement. For this purpose,
the lens potential applied to the deflector can be adjusted to
the ion optical effect of the parallelization magnet for each
beam deflection angle.
The Al+ ion dose D(x,z) has been calculated at each point
P(x,z) of the substrate surface, using a two dimensional
Gaussian beam current density distribution with σx and σz
as FWHM
j(x, z) =I
2πσxσz
exp[−1
2(x2
σ2x
+z2
σ2z
)],
according to
D(x, z) ≈1
∆x × f
2σz∑zp=−2σz
∫∞
−∞
j(xp, zp)dxp,
where a beam scan frequency of f = 33 Hz and a scanning
width of ∆x = 250 mm was chosen. The calculation is valid
for small distances ∆z ≪ σz between each scanned line,
which is satisfied at a substrate velocity of 200 mm/min re-
sulting in ∆z = 0.1 mm.
50
0
-650 -600 -550 -500 -450 -400 -350
UDefl = -/+ 4.2 kV
z [m
m]
x [mm]
ULens = - 15 kV UDefl = 0 kV ULens = - 24 kV
UDefl = -/+ 3.8 kV ULens = - 17 kV
Figure 6: 30 mA Al+ ion beam spot size on target at ± 10°
beam deflection, tuned with the deflector potential and the
deflector lens potential, respectively.
CONCLUSION
A new high current wide area metal ion implantation
platform for large surface applications has been developed.
It comprises a unique ECR metal ion source, which is
equipped with an integrated cylindrical sputter magnetron
as metal vapor supply, as well as beamline elements such as
an analyzing dipole magnet, an electrostatic deflector, and a
beam parallelization dipole magnet. Assuming a perfectly
stable current of 30 mA Al+ ions, an implantation dose of
2.25×1016 cm−2 can be reached with the facility according
to simulations. First experiments concerning the optimiza-
tion of the implantation platform are carried out at present.
A newly designed Faraday cup system is used to measure
the metal ion beam current. Its water cooled cup electrode
allows the application of a beam power above 1 kW.
REFERENCES
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[5] S. Humphries, J. Computational Phys., 125:448, 1996.
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Proceedings of IPAC2014, Dresden, Germany MOPRI085
04 Hadron Accelerators
T01 Proton and Ion Sources
ISBN 978-3-95450-132-8
811 Cop
yrig
ht©
2014
CC
-BY-
3.0
and
byth
ere
spec
tive
auth
ors